Aerodynamic shape optimization for alleviating dynamic stall characteristics of helicopter rotor airfoil

In order to alleviate the dynamic stall effects in helicopter rotor, the sequential quadratic programming （SQP） method is employed to optimize the characteristics of airfoil under dynamic stall conditions based on the SC1095 airfoil. The geometry of airfoil is parameterized by the class-shape-transformation （CST） method, and the C-topology body-fitted mesh is then automati- cally generated around the airfoil by solving the Poisson equations. Based on the grid generation technology, the unsteady Reynolds-averaged Navier-Stokes （RANS） equations are chosen as the governing equations for predicting airfoil flow field and the highly-efficient implicit scheme of lower-upper symmetric Gauss-Seidel （LU-SGS） is adopted for temporal discretization. To capture the dynamic stall phenomenon of the rotor more accurately, the Spalart-Allmaras turbulence model is employed to close the RANS equations. The optimized airfoil with a larger leading edge radius and camber is obtained. The leading edge vortex and trailing edge separation of the opti- mized airfoil under unsteady conditions are obviously weakened, and the dynamic stall character- istics of optimized airfoil at different Mach numbers, reduced frequencies and angles of attack are also obviously improved compared with the baseline SC1095 airfoil. It is demonstrated that the optimized method is effective and the optimized airfoil is suitable as the helicopter rotor airfoil.